1. Field of the Invention
The present invention relates to a process for preparing amines by catalytic cleaving of carbamates.
2. Discussion of the Background
The cleaving, i.e. the decarboxylation, of carbamates is a common process for preparing amines. The resulting amines are in turn starting compounds for numerous industrial intermediates and active pharmaceutical ingredients.
The general reaction mechanism of the cleaving of carbamates is described by Ewing et al. in their publication J. Amer. Chem. Soc. (1980) 102(9), 3072-3084:

The cleaving of carbamates in the presence of tetra-n-butylammonium fluoride (Bu4NF) is described by Jacquemard et al. in Tetrahedron (2004) 60(44), 10039-10047:

where                R=methyl, ethyl, tert-butyl, benzyl, allyl or phenyl,        R′ is alkyl or aryl,        R″ is hydrogen, alkyl or aryl.        
The general structure of the carbamates is described by Gaines in J. Org. Chem. (1985) 50, 410-411 as a mono-molecular zwitterion or disalt.
Japanese publication JP 2006-069941 A describes, inter alia, the thermal decomposition of carbamates to prepare isocyanates. In contrast, JP 2004-262892 A describes the thermal decomposition of carbamates in the presence of a tin catalyst and of a solid catalyst selected from silicates, silica gel and/or metal.
The decomposition of ammonium carbamate to ammonia and carbon dioxide is described by WO 2006/094541 A and EP 1 195 194 A.
The cleaving of carbamates in the presence of a tin catalyst is also described in JP 2004-262892 A. The use of iodine to cleave carbamates is described by Vatele et al. in Tetrahedron Letters (2003), 44(51), 9127-9129.